Post-release monitoring for Galerucella calmariensis L. and G. pusilla Duft, (Coleoptera: Chrysomelidae) is used to evaluate the success of purple loosestrife, Lythrum salicaria L., biological control programs throughout North America.  These two congeners are difficult to separate into species and it appears that species composition may be related to wetland characteristics and climatic factors.  The objectives of this study were to determine if sampling methods commonly used in post-release monitoring accurately estimate species composition and are not biased with respect to sex ratio.  We evaluated two relative sampling methods aggregation pheromone trap, and hand collection of adults, compared to an absolute sampling protocol to evaluate the relative sampling methods for bias.  In 2005 and 2006, we segregated the growing season into two distinct collection periods when: 1) overwintering adults, and 2) F₁ adults were present.  Species composition did not differ between overwintered adults and F₁ adults so samples for the entire season were combined for analysis.  In 2005 pheromone traps captured significantly more G. calmariensis (t₆=8.74, P<0.05) when compared to hand collection.  In 2006, there was no difference between hand collection and pheromone traps (t₇₁=1.29, P=0.2).  Absolute sampling in 2006 showed that hand collecting (t₂₁=0.59, P=0.56) and pheromone traps (t₂₁=1.33, P=0.2) were not biased with respect to species composition.  All sampling methods were unbiased with respect to sex ratios.  We concluded that pheromone traps and hand collection accurately estimate species composition as part of a post-release monitoring program for G. calmariensis and G. pusilla.